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WEATHER
Meteorology Study of weather
I. Basic Principles
A. Earth in space
1. earth – spins on own axis &
completes one rotation every 24
hrs. (causing day & night)
2. earth – takes 1 year to complete 1
orbit (revolution) around the sun
3. earth’s axis tilted: 1 hemisphere
receives more light causing
summer; less light – winter
a. equinox – sun directly overhead
on equator;
- autumnal equinox – Sept. 21
- spring (vernal) equinox – March
21
b.) solstice –when the sun’s overhead on:
- Tropic of cancer – summer solstice:
June 21st
- Tropic of capricorn – winter solstice:
Dec. 21st
Tilt/Seasons –
0:50
B. Atmosphere
- 310 miles
2000 oC or higher
-50 miles/ -120 oC
-31 miles/ 0 oC
-ozone layer
- 11 miles/ -80 oC
- weather takes place
1. troposphere – lowest region where
weather occurs; contains water vapor &
clouds; contains 78.08 % (78%) N2 and
20.94% (21%) O2
2. stratosphere – warmer due to ozone
(O3) layer; absorbs UV radiation
Our Atmosphere –
2:40
C. 3 causes of weather –
pressure, temp., precip.
II. Pressure
- downward force exerted by the weight
of the air; greatest at sea level;
measured by the weight of the air
(barometer)
A. Higher pressure has a higher temp.;
- less pressure - cooler; ex. mt., heat
pump
- less pressure – lets air rise faster to
make winds
B. Wind – air moves from a high to low
pressure (H  L)
Pressure moves from H  L
C. High pressure systems (H) – move
clockwise & generally result in fair
weather
D. Low pressure systems (L) – move
counterclockwise & generally result in
unsettled (bad) weather
E. Isobars – lines on weather maps to
connect similar pressures
Air Pressure – 2:11
High/Low Pressure – 1:00
III. Temperature Measure of amt. of energy of the
molecules; caused by sun;
measured by thermometer
A. Sunshine
1. warmth & light
2. photosynthesis – makes food & O2
3. helps in evaporation/transpiration drives the water cycle
4. creates optical effects
a. reflection – light bounces off a
surface; ex. oceans reflect light
- albedo effect – reflectiveness of a
surface; ex. snow & white shirt – high
albedo
b. refraction – light moving from 1
medium to another, causes the speed
to change & bends the light; ex. mirage
REFLECTION
REFRACTION
B. Conduction
1. Heat striking an object transfers
some energy to object; ex. sand gets
hot on feet
2. materials vary in amount of heat
absorbed (specific heat capacity)
before temp. increases; ex. metal heats
up faster than wood
C. Density of different temp.
1. heat – less dense, warm air rises
2. cold – more dense, cold air sinks
3. convection current – warm fluid that
is less dense & rises; ex. in
atmosphere, ocean, under the crust
D. Isotherms – bands used on
weather maps to connect similar
temps
Sunlight & Solar Energy –
1:49
E. Temperature Fronts
1. cold front – barometer falls – low;
large clouds form; violent storms –
thunder & lightning
2. warm front – less violent storms;
don’t move as fast but last longer; as
warm air rises, it cools & condenses 
precip.
Fronts – 3:17
IV. Water
A. Importance? Available
B. H2O & the weather – can
occur in all 3 states at ordinary
temps.
gas
boiling

condensation

liquid
melting

freezing

Solid (ice)
- takes a great deal of energy to change
the temp.
- oceans fluctuate less than land
- cold/warm ocean currents affect the air
temp. above it
C. Water Cycle
- 9 places water found: clouds,
groundwater, oceans, lakes,
rivers, soil, plants, animals,
glaciers
D. Clouds and Fog
1. Relative humidity: 100% - air becomes
saturated; fog – ground level; clouds –
above ground; warm air holds more
moisture than cold air
2. water vapor (normally) condenses only
onto a surface; ex. Dust, soot, sulfate the bigger the particle the bigger the
droplet; called CCN – cloud
condensation nuclei
E. Rain water droplets more than .5
mm across collects around CCN;
when too heavy they fall as rain
F. Snow & Sleet
1. Snow – water freezes to form
crystals
2. Sleet – ice pellets smaller
than 5 mm in diameter
G. Hail, thunder, lightning –
caused by rising warm air
1. Hail – rising air currents carry
water droplets up & they freeze.
This process continues &
refreezes in layers. When heavy
enough to overcome air currents,
they drop
2. Thunder & lightning – rising air
currents create convection currents –
hot air rises at center while cold air
sinks at sides
- thundercloud: has + electrical charge
at top & - charge at the bottom.
Eventually huge sparks flash between
the charges, neutralizing them 
lightning.
- Lightning releases so much energy –
that air which passes through it
explodes  thunder
- the difference in electrical charge
can be more than 305 volts/ft.
What are Thunderstorms? – 0:43
How do Thunderstorms form? –
2:41
Updrafts & Hail –
1:10
H. Dew & water Clear skies cause quick cooling,
chilling the air next to it. Water
vapor condenses on surface 
dew (dew point reached)
THE END!